Green’s Dictionary of Slang

1. (drugs) to place the last unsmoked portion of a cannabis cigarette into the end of a regular cigarette so as to make it more easily smokeable. A folded matchbook can be used for the same effect.

1962		(con. 1950s) H. Simmons Man Walking On Eggshells 165: She took a deep drag, put the joint out and cocktailed the roach in a cigarette.
1969		‘Iceberg Slim’ Pimp 177: The bomber in her hand was now a ‘roach’. I cocktailed it for her.

2. to lace a tobacco cigarette with cocaine.

2001

ONDCP Street Terms.